Mesoscopic texture at the skin area of mesophase pitch-based carbon fiber

The development of mesoscopic texture, which describes the structural units 10-100 nm in size, at the transverse skin area in mesophase pitch-based carbon fibers as a result of heat-treatment were examined using a high resolution scanning electron microscope (HR-SEM). The graphitized carbon fiber was found to be composed of plate-like mesoscopic structural units defined as rectangular microdomains whose dimensions were 20 nm thick, 30-50 nm wide, and 50-100 nm long along the fiber axis. Graphitized fibers spun at 300 and 310 °C contained microdomains which were usually arranged with their longer axis perpendicular to the fiber surface in the transverse skin area. Fibers spun at 300 and 310 °C exhibited radial and random cross-sectional textures in their major core areas, respectively. The longer edges of the domains and microdomains formed the tops of the fibril and microfibril, respectively, in the longitudinal surface. The graphitized fiber spun at 340 °C exhibited an onion-like texture in overall area and several layers of zig-zag microdomains formed the concentric surface. The encountering edge of two zig-zag microdomain units forming the top of fibrils exhibited smooth curvature where spurs run parallel along the fiber surface. The edge of rectangular microdomain faced directly to the surface in the carbonized fiber after the removal of the soluble component. Spurs in the surface were no longer observed to run parallel to the carbonized surface of the extracted fibers regardless of the transverse textures, suggesting that the basal planes observed in the surface of the unextracted fiber originate from the soluble fraction in the mesophase pitch.